1. Field of the Invention
This invention relates to a method of manufacturing a semiconductor device such as a semiconductor laser, a semiconductor photodetector, a semiconductor optical switch, a semiconductor optical filter, and a semiconductor optical modulator. More particularly, it relates to a method of manufacturing a semiconductor optical device in which a semiconductor device can be manufactured by a self-alignment process. The present invention also relates to a gyro that can be prepared by using such a method.
2. Related Background Art
Conventionally, semiconductor optical devices are manufactured by forming a semiconductor layer that provides intended functions, such as light emission, light detection, light guidance and modulation, on a substrate by means of crystal growth, subsequently etching the device to the size and the shape designed to substantiate the intended functions and finally forming electrodes. See, inter alia, Japanese Patent Application Laid-Open No. 5-7019.
However, when the size of electrodes formed is small, known methods of manufacturing semiconductor optical devices are accompanied by the difficulty of alignment in the photolithography processes. For instance, it is extremely difficult to form a 4 xcexcm wide electrode on a 5 xcexcm wide mesa with any known method of manufacturing semiconductor optical devices.
Additionally, known methods of manufacturing semiconductor optical devices involve the step of forming an etching mask such as a photoresist on a semiconductor layer followed by etching the semiconductor layer and removing the etching mask. With such a technique, the semiconductor layer is often contaminated during the process between the application of an etching mask such as a photoresist and the removal thereof, making it difficult to achieve a good ohmic contact when forming an electrode. While a good ohmic contact can be established by using an additional process of etching the semiconductor layer for the purpose of eliminating the contaminated part of the semiconductor layer in the electrode-formed area, the additional process is disadvantageous in terms of increased process steps.
Therefore, it is an object of the present invention to provide a method of manufacturing a semiconductor optical device that can eliminate the need of aligning a mesa and an electrode to be formed on a mesa.
Another object of the present invention is to provide a gyro comprising a ring-resonator type semiconductor laser in which beams circuitally propagate in opposite directions by using the above manufacturing method.
According to the invention, there is provided a method of manufacturing a semiconductor device comprising the steps of:
preparing a member having at least one semiconductor layer on a substrate;
forming an electrode layer on the semiconductor layer;
forming an etching mask on the electrode layer; and
forming a mesa profile by etching the electrode layer and the semiconductor layer.
According to an aspect of the invention, said semiconductor layer has a multilayer structure.
According to another aspect of the invention, said semiconductor layer and said electrode layer each comprising said mesa profile have the same width.
The member is a wafer having at least one semiconductor layer.
According to the invention, there is also provided a method of manufacturing a semiconductor optical device comprising:
a first film forming step of forming at least one semiconductor layer on a substrate;
a second film forming step of forming a film of a first electrode material on said semiconductor layer;
a third film forming step of forming a protection film on said first electrode material;
a step of selectively forming an etching mask;
a first etching step of selectively etching the protection film;
a second etching step of selectively etching the first electrode material;
a third etching step of etching the semiconductor layer to a predetermined depth;
a step of removing the etching mask and the protection film; and
a step of forming a second electrode on the substrate.